Reciprocating fluid motor



c. L.. ENGLISH 3,204,535

RECIPROCATING FLUID MOTOR 4 Sheets-Sheet 1 sept. 7, 1965 Filed Feb. l5, 1962 Sept. 7, 1965 c. l.. ENGLISH 3,204,535

RECIPROCATING FLUID MOTOR Filed Feb. 15, 1962 4 Sheets-Sheet 2 W1.... 2,., .Ilm 52111 fffffffvz m, .mmmm.. .2.. ,lrrffJ/i 2r W. M r/afw 5 5%@ 2L 6 5 7/\7 m J 2 FIETS Fig-5 Sept 7, 1965 c. L. ENGLISH 3,204,535

RECIPROCATING FLUID MOTOR Sept. 7, 1965 c. ENGLISH REGIPROCATING FLUID MOTOR 4 Sheets-Sheet 4 Filed Feb. 13, 1962 INVE R.n CHARM-5 e /v ./sH

United States Patent 4O .3,204,535 RECIPRGCAIING FLUID MOTOR Charles I... English, 2204 E. th Place, Tulsa, Okla. Filed Feb. 13, 1962, Ser. No. 172,947 S Claims. (Cl. 91-222) This invention relates generally to improvements in subsurface pumps utilized in oil wells and the like and more particularly, but not by way of limitation, relates to fluid operated subsurface pumping units and to an improved uid motor therefore.

Subsurface fluid operated pumping units have been known in the oil producing industry for many years. A complete pumping unit comprises a fluid operated motor and a reciprocating type pump connected in tandem relation, the entire pumping unit being of suiciently small diameter as to be lowered through the wellbore to the producing formation. In the operation of such pumping units, a power fluid, normally clean oil, is pumped under relatively high pressure downwardly to the fluid operated motor of the pump unit which is reciprocated by the power fluid to thereby operate the pump. The well fluids, together with the used or exhaust fluid from the motor which is mixed with the well fluids, are thereby pumped upwardly to the wellhead. The subsurface pumping units may be either of two types known generally in the art as the insert type or the free type. An insert type pumping unit is suspended on the lower end of a string of relatively small diameter tubing through which power fluid is pumped downwardly to the liuid operated motor. The well uid and exhausting power fluid from the motor are directed upwardly through a larger string of tubing encircling the insert tubing string or through the well casing in which the pumping unit is seated. On the other hand, a free type pumping unit is provided with suitable cups of a size such that the pumping unit can literally be pumped downwardly and upwardly through one string of tubing to and from a pump cavity. The pump cavity communicates with another string of tubing extending to the wellhead. The pumping unit can then be pumped upwardly by directing fluid downwardly through the separate string of tubing into the pump cavity below the pumping unit. In order to operate the free type pumping unit, the power oil is forced down one of the tubing strings, while the pumped well fluids and exhausting power fluids are forced upwardly through the other tubing.

In copending application Serial No. 89,053, filed February 13, 1961, now Patent No. 3,109,379, several embodiments of complex fluid motors are disclosed which have two pistons connected in tandem and have various valving arrangements for operating the complex iluid motors. In all subsurface pumping units of this type, it is rather apparent that the diametrical dimensions of the hydraulic pumping unit are limited by the diameter of the well in which the pump is to be used. Frequently in the deeper wells, and particularly in cases where the well has multiple completions, production from the lower producing formations will necessarily be through very small tubing or casing strings. Frequently, the diameter of the pump is as small as 1% inches. referred to above, the complex Huid motors described provide a piston member having an increased working area for increasing the horsepower produced by the motor without increasing the pressure of the power fluid.

The present invention contemplates a novel and highly eilicient subsurface pumping unit, and more particularly, contemplates an improved novel fluid motor of the general type described in the copending application referred to above wherein the effective working area of the piston member is further increased by a novel valving arrangement in combinati-on with the piston member. This in- In the copending application ICC vention further contemplates, within the piston member, a novel pilot valve arrangement for controlling a main valve, and a novel means for shifting the pilot valve in order to cause reciprocation of the piston member.

Therefore, an important object of this invention is to provide a subsurface fluid operated pumping unit which will eciently and economically produce an oil well having substantially any production and horsepower requirements.

Another object of this invention is to provide a reciprocating pump unit having the eiciencies and the economies of a single-acting pump unit, but having the capacity of a double-acting pump unit.

Another object of this invention is to provide an improved subsurface fluid motor for reciprocating a subsurface uid pump wherein the power produced on the upstroke is substantially equal to the power produced on the dowustroke, and the total power produced is substantially the maximum for a given diameter motor and given power fluid pressure.

A further object of this invention is to provide an improved four-way valving arrangement in the piston head of the fluid operated motor.

Still another object of this invention is to provide an improved four-way valve in the piston which is very economical in construction.

Another object of this invention is the provision of a highly useful pilot valve assembly which may be utilized to hydraulically shift a main valve to produce reciprocation of a motor piston member.

A still further object of this invention is to provide a four-way valve of the type described which utilizes a minimum of space whereby the greatest operating etliciencies can be produced.

Many additional objects and advantages will be evident to those skilled in the art from the following detailed description read in the light of the accompanying drawings.

In the drawings:

FIGS. 1, 2, 3 and 4 taken together comprise a longitudinal sectional view of a pumping unit constructed in accordance with the present invention. It will be noted that FIG. 1 is taken on lines 1 1 of FIG. 8, and FIG. 2 is taken on lines 2 2 of FIG. 10, in order to better illustrate the operative details of the pumping unit.

FIG. 5 is a longitudinal sectional view of the lower motor piston of the fluid motor of the pumping unit of FIGS. 1-4 with the valving assembly in position for causing an upstroke of the piston member, and is taken substantially on lines 5 5 of FIG. l1.

FIG. 6 is a longitudinal sectional view substantially identical to that of FIG. 5, except that the valve assembly is shifted to cause a downstroke of the piston member.

FIG. 7 is a sectional view through a portion of the lower motor piston showing the pilot valve mechanism in the upper position, and is taken substantially on lines 7 7 of FIG. 10.

FIG. 8 is a cross sectional view taken substantially on lines 8 8 of FIG. l.

FIG. 9 is a cross sectional View taken substantially on lines 9 9 of FIG. 2.

FIG. 10 -is a cross sectional View taken substantially on lines 1(9 16 of FIG. 2.

FIG. 11 is a cross sectional view taken substantially .on lines 11-11 of FIG. 2.

FIG. l2 is a cross sectional View taken substantially on lines 12-12 of FIG. 2.

As mentioned previously, a iluid operated subsurface pumping unit is shown in longitudinal section by the FIGS. 1-4. The pumping unit is comprised generally of a complex fluid motor unit 18, which includes generally the structure shown in FIGS. 1 and 2, and a complex pump unit 20, which includes generally the structure shown in FIGS. 3 and 4. It will be appreciated that the length of the pumping unit illustrated in FIGS. l-4 is substantially reduced for convenience of illustration. In actual practice, the pumping unit may be some twenty feet in length while having a diameter less than two inches. The pumping unit is of the insert type and may be lowered through a larger string of tubing or casing by a separate, insert tubing string 21. The power fluid is then pumped downwardly through the insert tubing string ZIv/hich is connected in the adapter 22. The spent power fluid or exhaust fluid from the tiuid motor, together with the well duid, is pumped through the production bores 35 (see FIG. 3) and upwardly through the annulus around the insert tubing string 21, by the pump unit 20, as hereafter described in greater detail.

The complex fluid motor 18 is comprised generally of upper and lower motor-cylinders 23 and 24, respectively, in which upper and lower motor pistons 25 and 26, respectively, are reciprocally disposed. The upper motor piston 25 divides the upper motor cylinder into upper and lower cylinder chambers 23a and 23b, respectively. The lower motor piston 26 divides the lower motor cylinder 24 into chambers 24a and 24h, respectively. The motor pistons 25 and 26 are interconnected in tandem relationship by a tubular motor piston rod indicated generally by the reference numeral 27, and hereafter described in greater detail.

The upper motor cylinder 23 is formed by the adapter 22, which has a small diameter neck 27 threaded into an inner cylinder sleeve 28 by threaded coupling 29. An outer cylinder sleeve 30 is also threaded onto the adapter 22 by threaded coupling 36a and is concentrically disposed around the inner cylinder sleeve 23 to form an annular fluid passageway 31. A plurality of bores 32 provide iiuid communication between the interior of the insert tubing string 21, which is threaded into the adapter 22, and the annular passageway 31. The lower end of the router cylinder sleeve 36 is threaded onto the tubular body 33 of a packing assembly 34 by threads 36. A retainer ring 38 is threaded into the packing housing 34 and compresses a resilient packing 40 into sliding, peripheral sealing engagement with the tubular piston rod 27.

The lower motor cylinder 24 is formed by the packing assembly 34, a tubular lower cylinder sleeve 43, which is connected to the packing assembly 34 by threaded coupling 44, and a second packing assembly 46 which is connected to the lower end of the lower cylinder sleeve 43 by threaded coupling 48. A retainer ring 49 (see FIG.

l3) is threaded into the packing assembly body 50 and y compresses a resilient sealing ring S2 into sliding, peripheral sealing engagement with a tubular connecting rod 54 which interconnects the motor pistons 25 and 26 and the pump pistons hereafter to be described.

The complex pump unit 20 has upper and lower pump cylinders 55 and 56 in which upper and lower pump pistons 57 and 48, respectively, are reciprocally disposed. The pump pistons 57 and 58 are interconnected by a tubular pump piston rod 59. The upper pump piston 57 divides the upper pump cylinder into upper and lower chambers 55a and 55h, respectively; and the lower pump piston 58 divides the lower pump cylinder 56 into upper and lower chambers 56a and 56h, respectively.

The upper pump cylinder 55 is formed by the packing assembly 46, a third tubular sleeve 60, and a third packing assembly 61. The third tubular cylinder sleeve 60 is connected to the lower end of the packing assembly body 50 by the threaded coupling 58. The lower end of the cylinder sleeve 60 is connected to the packing assembly 61 by threaded coupling 62. A retainer ring 64 is threaded into the packing assembly 61 and compresses a resilient packing 66 into peripheral sealing engagement with the pump piston rod 59.

The lower pump cylinder 56 is formed by the packing assembly 61 and a fourth tubular cylinder sleeve 68 which is connected to the packing assembly body 61 by threaded coupling 70. The lower end of the cylinder sleeve 63 is connected by threaded coupling 76 to a standing valve housing indicated generally by the reference numeral 74. The standing valve assembly '74 may be of any conventional type and is illustrated as having a seating nipple 73 for insertion in an appropriate hold down shoe or other pump cavity facility in the bottom of the casing string. The seating nipple 78 is threaded into the body 79 of the standing valve assembly 74 to retain a standing valve cage Sil in position in the assembly '74. A valve body S2 contacts the seat 84 of the valve cage 30 to form a seal and block downward passage of iiuid through the standing valve assembly '74 in the conventional manner.

The two fluid motor piston members 25 and 26 which are reciprocally disposed within the motor cylinder sleeves 28 and 43, respectively, are provided with a plurality of conventional piston rings 98 and 1%, respectively, to provide a peripheral sliding seal between the respective pistons and cylinder sleeves in the conventional manner. The connecting rod assembly 27 interconnecting the motor pistons 25 and 26 is comprised of an inner tubular member 1t6having a passageway 1t6a which is connected to the body 197 of the upper motor piston 25 by threaded coupling 10S at the upper end thereof, and is connected to the lower motor piston 26 by threaded coupling 116. Another tubular sleeve 112 is concentrically disposed around the tubular member 106 to form an annular iluid passageway 113 therebetween and is connected to the piston body 107 by threaded coupling 114. The outer tubular member 112 passages through the resilient packing member 40 which provides a iluid-tight sliding seal therearound. A plurality of apertures provide fluid communication between the chamber 24a and the annular passageway 113 formed between the tubular rod 106 and the tubular member 112.

High pressure power Huid passing down through the insert tubing string 21 passes through the bores 32, through the annular passageway 31 between the tubular sleeves 28 and 30, and through the orices 11S into the chamber 23]). The lower end of the piston body 167 is squared at 120, as can best be seen in FIG. 8, and is provided with four radial bores 122 which communicate with the interior of the tubular connecting rod 166. Therefore, high pressure uid from the insert tubing string 21 is continually introduced to the chamber 2311 below the upper piston 25, and passes through the bores 122 into the interior passageway 106a of the tubular connecting rod 106.

A large bore 124 (see FIG. l) and tour smaller bores 126 as best seen in FIG. 8, provide a iiuid passageway means between the chamber 23a above the upper motor piston 25 and the annular passageway 113 which is formed between the tubular rod members 106 and 112. As previously mentioned, the annular passageway 113 is in continuous iluid communication with the charnber 24a above the lower motor piston 26 through the apertures 116.

The lower motor piston 26 contains a main valve, indicated generally by the reference numeral 13d, which is disposed within a main valve cavity, indicated generally by the reference numeral 132, which is formed in the body 133 of the lower motor piston. The main valve cavity 132 is formed by a first bore 134, a slightly larger counterbore 136, and the interior bore 137 ot a plug member 138 having a sleeve 140 inserted in the counterbore 136. The body ot the plug member 138 is received in still another counterbore 142 and is held in place by a retainer plug 144 which is connected to the body 133 by the threaded coupling 146. It will be noted tha' the tubular connecting rod 106 is threaded into the retainer plug 144. The diameter of the bore 134 is less than the diameter lof the bore 137 in the sleeve insert 149, which in turn is less than the diameter of the bore 136.

aso/1,535

The bore 136 is enlarged by undercutting to form similar annular passageways 150 and 152. The passageway 152 is best shown in FIG. l0, and the passageway 150 is of substantially the same cross sectional outline. It will be noted that the annular passageways 150 and 152 are spaced apart so that an annular seating land 154 is formed between the annular passageways which coacts with the main valve 130 as hereafter described in greater detail.

The upper annular passageway 150 in the main valve cavity 132 intersects four longitudinally extending bores 156 in the piston body 133 which register with four similar bores 158 in the plug insert 138, and which in turn are in fluid communication with the interior passageway 106:1 of the tubular lconnecting rod 106 through the countersunk bore 159 and the bore 144a in the plug insert 144. The lower annular passageway 152 intersects the upper ends of four bores 160 (see FIG. 10) which are in constant fluid communication with the chamber 24h of the cylinder sleeve 42 below the lower motor piston 26.

An upper set of radial bores 162 in the piston body 133 register with bores 163 in the sleeve insert 146, and provide a fluid passageway means between the main valve cavity and the chamber 24a in the cylinder sleeve 43 above the piston 26. A similar lower set of radial bores 164 in the piston body 133 register with bores 165 in the sleeve insert 140 to also provide fluid communication between the main valve cavity 130 and the chamber 24a. The lower set of bores 164 and 165 are shown in FIG. 1l which also shows an annular passageway 166 which may conveniently be formed by an offset counterbore to the counterbore 136 in the piston body 133. The annular counterbore 166 provides fluid communication between the several bores 164 and 165 for increasing the efficiency of the uid motor. A similar annular passageway, not designated by reference numeral, may be associated with the bores 162 and 163.

The main valve 130, which may be classified generally as a four-way, differential area, sleeve type valve, is reciprocally received within the main valve cavity 132. The lower end of the main valve cavity 132 is in direct communication through the axial bore 169 in the piston body 133 with the interior of the tubular connecting rod 54 which, as hereafter described in greater detail, is the exhaust passageway for used power fluid. The main valve 130 is a single piece tubular member having an interior passageway 170 extending from end to end. The interior passageway 170 of the main valve is continuously in uid communication with the interior of the connecting rod 54. The main valve 130 is comprised generally of: a lower portion 172, which is slidingly received in the counterbore 134 and is sized to provide a peripheral iuidtight seal; a central portion 174, which is received in the counterbore 136 and is sized to provide a peripheral uidtight seal therewith; and an upper portion 176, which is slidingly received in the bore 137 in the insert sleeve 140, and is sized to provide a peripheral iiuidtight seal therewith. An annular groove 17S is provided between the portions 174 and 176 which is of smaller diameter than the bore 137 in the sleeve insert 140 to provide a peripheral fluid passageway for purposes which will hereafter be apparent. A plurality of radial bores 180 in the central portion 174 (see FIGS. 2, 5 and 6) provide fluid communication between the passageway 170 and the annular passageway 152 as hereafter described.

The main valve 130 is so dimensioned that when it is in its lower position, shown in FIGS. 2 and 5, the bores 163 will be uncovered and provide a fluid passageway from the chamber 24a through the bores 162 and 163 to the interior of the valve chamber 132, and then through the passageway 170 down to the exhaust passageway 54a in the connecting rod 54; the portion 176 will co-ver and close the radial bores 165; the annular groove 178 will register with both the annular passageways 150 and 152 to provide fluid communication between the power iluid bores 156 and the bores 160; and the radial apertures 160 in the valve body will be received within the bore 136 and thereby closed. When the main valve is in its uppermost position, as shown in FIG. 6, the upper portion 176 will cover and close the radial bores 163; the annular groove 178 will register with both the annular passageway and the radial bores 165 to provide fluid communication between the power fluid bores 156 and the chamber 24a above the piston 24; the portion 174 will be received in the annular seating land 154 to prevent downward passage of fluid from the .annular passageway 155); and the radial apertures 18) will register with the annular passageway 152 to provide fluid communication between the chamber 24b and the interior passageway 170 =of the valve body 130, and therefore with the exhaust uid passageway 54a in the connecting rod 54.

To summarize that portion of the pumping unit described above, it will be noted that power liuid pumped down through the insert tubing string 21 will at all times be introduced to the chamber 23h and to the power fluid bores 156 of the main valve cavity 132 through fluid passageway means comprised of the bores 32, the annular passageway 31, the -apertures 11S, the chamber 23h below the piston 23, the radial bores 122, the interior passageway 166e of the tubular connecting rod 106, the bores 158 and 156, and the annular passageway 150. When the main valve 130 is in the lower position, `as shown in FIGS. 2 .and 5, the high pressure power fluid will then pass to the chamber 24h through passageway means comprised of the annular groove 17S, the :annular passageway 152, and the bores 160. Therefore, it will be seen that when the mai-n valve 130 is in the lower position, high pressure will fill both the lower chambers 23b and 24b and will act on the downwardly facing working areas of the upper motor piston 23 :and the lower motor piston 24, respectively. The chamber 23a above the upper motor piston 23 is always in fluid cmrnunication with the chamber 24a above the lower motor piston 24 through the fluid passageway means comprised of the bore 124, the bores 126, the annular passageway 113, and the apertures 116. When the main valve 130 is in the lower position, the chamber 24a, and therefore the chamber 23a, is in fluid communiication with the exhaust port 54a in the tubular connecting rod 54 through fluid passageway means comprised of the radial bores 162 and 163, the upper end of the main valve cavity 132, and interior passageway 170 through the main valve 130. Therefore, the net hydraulic force on the motor pistons 23 and 24 is directed upwardly due to the high pressure power iiuid below each of the pistons acting against low pressure exhaust uid above each of the pistons, which results in an upstroke of the piston assembly.

On the other hand, when the main valve 130 is shifted to its up position, as shown in FIG. 6, the high pressure power fluid in the .annular passageway 150 cannot pass downwardly to the annular passageway 152 and through the bores 169 tothe chamber 24h because the portion 174 of the main v-alve 130 is disposed in the annular seating land 154. Instead, the power uid as directed to the upper chambers 24a and 23a by uid passageway means comprised of the circumferential groove 178, the bores and 164, the chamber 24a, the apertures 116, the annular passageway 113, and the bores 126 and 124 to the chamber 23a. At the same time, uid in the lower :chamber 2411 is vented to the exhaust passageway 54a through passageway means comprised of the bores 160, the annular passageway 152, the radial bores 180 and the passageway in the main valve 130. Although high pressure power fluid fills both the upper and lower cavities 23a and 23h, the upwardly facing working area of the upper motor pistion 23 exposed to the high pressure power fluid in the upper chamber 23a is greater, by the cross sectional area of tubular rod 27, than the downwardly facing workin-g area of the motor piston 23 which is exposed to the 4power fluid in the chamber 2311. Therefore, the net hydraulic force acting on the upper motor piston 23 will be downward, and will be equal to the pressure of the power uid times the cross sectional area of the tubular rod 27. The fluid within the lower chamber 2411 is in communication with the exhaust passageway 54a within the connecting rod 54. Therefore, the net hydraulic force on both the upper yand the lower motor pistons 23 and 211iI is directed downwardly, so that a downstroke of the pistons results. ln summary, it will be noted that when the main Valve 15) is in the down position, an upstroke of the motor pistons 23 `and 24 results; and when the main valve 13@ is shifted to the up position, a downstroke of the motor pistons results.

The main valve 136B is shifted tio and held in either the lower or upper position to cause reciprocation of the pistons by hydraulic fluid in a valve shifting cavity 264 (see FIG. 2) as will presently `be described. As previously mentioned, the diameter of the upper portion 176 of the main valve 136 is greater than the diameter of the lower portion 172 but less than the diameter of the central portion 174. Assume for the moment, as will generally be the portion 174 is greater than the area of the lower portion 172 by some unit area value, and is less than the area of the central portion 176i by the same unit area value. Then, noting that both ends 200 and 261 of the main Valve 130 are continuously exposed to low pressure exhaust fluid, the net hydraulic force on the ends 201i and 201 is one unit area of low pressure always acting downwardly on the end 26). High pressure power fluid is continually present in the annular groove 178, so that a` net hydraulic force equal to one unit area of high pressure power fluid is always acting downwardly on the shoulder 292 of the annular groove 178. At the same time, a shoulder 2il3, between the lower portion 172 and the central portion 174, which is two unit areas in size, is subjected so the pressure of the fluid in the valve shifting cavity 204. Therefore, when the fluid in the valve shifting cavity 204 is at low exhaust pressure, the force acting downwardly on the main valve 13d will be one unit of low exhaust duid pressure, plus one unit `of high power fluid pressure, which will be greater than the two units of low exhaust fluid pressure acting upwardly on the shoulder 203. Therefore, the main valve 130 will be shifted to and maintained in the down position to cause an upstroke of the piston as heretofore described. However, when the pressure in the valve shifting cavity 2M is increased to high power pressure, the two unit areas of high power pressure of the shoulder 203 will be greater than the combined total of one unit of high power pressure and one unit of low exhaust pressure, and the main valve 130 will be shifted to and maintained in the up position, to cause a downstroke of the piston members. The pressure of the fluid in the valve shifting cavity 264, and therefore the recipnocation of the piston, is controlled by a pilot valve assembly presently' to be described.

T he pilot valve assembly for controlli-ng the pressure of the fluid in the main valve shifting cavity 264 is illustrated in FIGS. 5, 6 and 7, with reference also being made to the cross sectional views of FIGS. 8, 9, 10, 11 and 12. A pilot valve cavity is in constant communication with the valve shifting cavity 204 through a passageway 205. rThe pilot valve cavity is `formed by a bore 266 drilled in the body 133 of the lower motor piston 24 from the top downwardly. The bottom of the bore 206 forms a shoulder 20S for arresting the downward travel of the pilot valve assembly as shown in FIG. and hereafter described. 1t will also be noted that the bore 206 is in huid communication with the chamber 241]), and that a portion of the pilot valve assembly hereafter described resting on the shoulder 203 will engage the upper end 211 (see FIG. 2) of the packing housing d6 and be moved upwardly, as hereafter described in greater detail. A counterbore 212 having a diameter larger than the diameter of the bore 206 is drilled downwardly from the top of the piston body 133. The upper end of the counterbore 212 is closed by the insert member 138.

A huid passageway 214 in the insert member 138 cornmunicates with a fluid passageway 216 in the retainer plug 14d through the facility of an annular passageway 217, which eliminates the necesssity of aligning the passage- Ways 214 and 216. The passageway 216 in tur-n is in fluid communication with a ball valve cavity 218, and then with the high 4pressure power duid in the interior passage- Way 16a of the tubular connecting rod 106 by means of the oounterbore 159. A ball-type valve 222 is seated for upward closing in the ball-valve cavity 218. A Istriker pin 224 is reciprocally disposed in the retainer plug 144, and is positioned to be moved downwardly to unseat the ball valve 222 when the lower motor piston 24 reaches the upper limit of its travel by a mechanism hereafter described.

The pilot valve assembly, indicated generally by the reference numeral 225, is comprised of a lower striker member 226 which is reciprocally disposed in the bore 296 of the pilot valve cavity. Of course, the lower striker member 226 is received in close tting sliding engagement with the bore 206 to provide a peripheral iluid seal. The upper end 228 of the lower striker member 226 is of a reduced diameter to permit uid to pass therearound as hereafter described. An upper pilot valve member 230 is slidingly received in the -counterbore 212 and is sized to provide a peripheral lluid seal with t-he counterbore 212.

An annular grooves 232 is formed at a midpoint lof the upper pilot valve member 230. The annular groove 232 is in fluid communication with the pilot valve cavity above the upper pilot valve member 231) by means of a fluid passageway 234. The upper end of the upper pilot valve member 230 is provided with a series of projections 336 which insure that the passageway 234 is not sealed by contact of the pilot valve member 230 against the insert member 13S. A sleeve 338 having a restrictive orifice therein is inserted in a lcounterbore to the fluid passageway 234 and greatly restricts the quantity of uid which may pass through the passageway 234 and thereby causes a :substantial pressure drop thereacross.

A high pressure power uid port 2st-ll (see FIG. 7) is formed by a boire in the body 133, which bore is closed by .a small plug 242. The high pressure power fluid port 245i) is in fluid communi-sation with ione of the high pressure power uid bores 156 by a passageway 244, which can best be seen in FIG. ll. An upper high pressure port 246 and `a lower high pressure port 248 provide fluid cornmunication between the high pressure power fluid port 240 and the 4counterbore 212 .and bore 20,6, respectively, of the pilot valve cavity. A low pressure exhaust luid port 25) is formed by drilling a bore, from the bottom, in the body 133 of the lower motor piston 24 and closing the bore with a plug 252. The low pressure exhaust lluid port 25@ is in continuous fluid communication with the pilot valve cavity through upper and lower low pressure ports 254 Iand 256. The lower end of the low pressure port 256 is also in continuous duid communication with the exhaust fluid passageway 54a of the tubular connecting rod S4 by a passageway 25S, which can best be seen in FIG. 12, but also may be located in FIG. 7 and in dotted outline i-n FIG. l0.

When 'the pilot valve assembly is in its lowermost position, as shown in FIG. 6, and the piston approaches the end of the downstroke, the lower pilot valve striker member 226 will be mechanically moved upwardly as the lower end thereof engages the upper face 211 of the packing housing 46. Similiarly, at the top of the upstroke, the striker pin 2.24 will be moved downwardly to unseat the ball valve 222 by a mechanism comprised of an annular washer 260 (see FIG. 2) which encompasses the tubular connecting rod member 106, and is biased upwardly into contact with the lower end of the tubular rod member 112 by Ia coiled spring 262. As the lower motor piston 9 24- approaches the top of the upstroke, the washer 260 will strike the shoulder 264 on the lower end Iof the packing housing 34, and the washer 260 will be forced downwardly to move the striker pin 224 downwardly and unseat the ball valve 222 and thereby shift the pilot valve assembly downwardly as hereafter described.

Referring once again to FIGS. 3 and 4, as previously mentioned the pumpis comprised generally of the upper pump cylinder 55, in which the upper pump piston 57 reciprocates, and the lower pump cylinder 56, in which the lower pump piston 58 reciprocates. The reciprocation of the fluid motor is transmitted through the tubular connecting rod 54, which as previously mentioned, has an interior passageway 55 for the exhaust uid from the fluid motor. The tubular connecting rod 54 is connected by a threaded coupling 270 the upper pump piston 57. The interior of the connecting rod 54 is in liuid communication with the chamber 55a above the upper pump piston 57, through passageway means comprised of an undercut cavity 271 and a plurality of bores 272. A bore 273 communicates with the bores 272 and in combination therewith constitutes a uid passageway through the upper pump piston 57.

A conventional downwardly closing traveling valve assembly indicated generally by the reference numeral 274, is disposed in the bore 273 and is comprised of a spider 276 which slidingly retains the stem 278 of a valve body 280. The valve body 280 seats on the annular seating surface formed on the spider member 276 and constitutes a downwardly closing check valve. The spider assembly 276 is retained within bore 273 of a tubular adapter 280 which is connected to the body of the upper pump piston 57 by a threaded coupling 282. The lower tubular connecting rod 59 having an interior uid passageway 59a is then connected to the tubular adapter 280 having an interior passageway 28th by a threaded coupling 284. A plurality of bores 380 in the tubular adapter 280 provides continuous fluid communication between the interior passageway 288er and the chamber 55b below the upper pump piston 59. The lower end of the tubular connecting rod 59 is connected to the lower pump piston 58 by threaded coupling 286. The interior passageway 59a of the lower connecting rod 59 is in liuid communication with the interior passageway 280:1 and with a bore 288 which extends through the lower pump piston 58 and is in fluid communication with the chamber 56b below the pump piston 58. A uid passageway 290 is also provided to establish fluid communication between the passageway 288 and the chamber 56a above the lower pump piston 58. An upwardly closing ball-typecheck valve 292 is provided in the passageway 290 to check uid passing upwardly through the passageway 290. The valve 292 is urged upwardly into seating engagement by a spring biased cradle member 294 having a shank 296 which is received in the bore of an insert 298. A coil spring 299 biases the cradle member 294 upwardly to seat the valve 292. i

Operation When utilizing the pumping unit to produce an oil well, the pumping unit is lowered into a string of tubing or casing having an internal diameter greater than the external diameter of the pumping unit by an insert string of tubing 21. The pumping unit is lowered until the seating nipple 78 is properly inserted in a seating shoe disposed in the casing at the producing formation. Power fluid can then be pumped downwardly through the insert tubing string 21 to operate the fluid motor 18. Exhaust fluid from the uid motor 18, together with the well uids, exit through the bores 35 and is pumped upwardly through the annulus between the insert tubing string 21 and the casing or tubing string containing the pumping unit. Prior to the introduction of power fluid to the insert tubing string 21, gravity will, in most cases, cause the four interconnected piston members 25, 26, 57 and 58 to rest at the lower limit of their travel. Also, the main valve will be in its lower position, as shown in FIGS. 2 and 5. Since the lower motor piston 26 is sufciently lowered that the neck 209 will be received in the well 210 in the packing housing 46, the upper end 211 of the packing housing will contact the lower end of the lower pilot valve member 226, and the pilot Valve assembly will be held substantially in the upper position, as shown in FIGS. 5 and 6.

Therefore, when power fluid is first pumped downwardly through the insert tubing string 21, the high pressure power duid will be applied to the chamber 23b and to the annular passageway of the main valve cavity 132 through passageway means comprised of the bores 32, lthrough the annular passageway 31, and the orifices 118, into the chamber 23b, and the radial bores 122, the interior passageway 106a in tubular piston rod 106, and the bores 158 and 156 which lead to the annular passageway 150. Since the main valve 130 is in the lower position, the power iiuid will be directed by the annular groove 178 to the annular passageway 152 and into the chamber 24b below the lower motor piston 26 by the passageway means comprised of the bores 160. Also, with the main valve 130 in the lower position, the iluid within the chamber 23a above the upper motor piston 25, and the fluid within the chamber 24a above the lower motor piston 26, will be in communication with the eX- haust fluid passageway 54a in the connecting rod 54 through fluid passageway means comprised of bores 124 and 126, the annular passageway 113, and the orifices 116 down to the chamber 24a, and then the radially extending bores 162 and 163, and the interior passageway of the main valve 130. The exhaust fluid continues downwardly through the interior passageway 54a in the connecting rod 54 to be commingled with well iiuids in the passageway 272 and pumped outwardly through the apertures 35 and upwardly through the annulus around the insert tubing string 21. Therefore, the net hydraulic force on both the upper motor piston 90 and the lower piston 92 is directed upwardly to cause an upstroke of the fluid motor, as previously described.

It will be noted that when the main valve 130 is down and the pilot valve assembly 225 is up, as would be the condition at the start of operation, neither of the valves Y will be appreciably shifted by the introduction of power uid until the top of the upstroke is reached. This will be evident because the valve shifting cavity 204 is in fluid communication with the exhaust fluid passageway 54a through passageway means comprised of the passageway 205, the pilot valve cavity, the passageway 255, the low pressure port 250, and the passageway 258. With regard to the pilot valve assembly 225, the high pressure in the passageway la will enter through the passageway 218 and seat the ball valve 222 to assure that high pressure fluid will not be applied to the upper end of the pilot valve member 230. At the same time, the pressure above the upper pilot valve member 230 is vented to the low pressure exhaust port 250 through the orifice sleeve 338, the passageway 234, and the bore 254. The upper and lower high pressure ports 246 and 248, which communicate with the high pressure power liuid port 240, are closed by the upper pilot valve member 230 and the lower pilot valve member 226, respectively. Therefore, the net hydraulic force on the pilot valve assembly 225 is upwardly because all parts of the pilot valve assembly are subjected to low or exhaust pressure, except the lower end of the lower pilot striker member 226. The lower end of the lower pilot valve striker member 226 is subjected to high pressure power iluid within the chamber 24b, which urges the entire pilot valve assembly into the upper position shown in FIGS. 5 and 6. The pilot valve assembly will be maintained in the upper position by this hydraulic bias throughout the upstroke of the pistons.

During the upstroke of the pump pistons 57 and 58, the traveling valve 274 will be closed and all fluid in the chamber 55a above the upper pump piston 57, including all exhaust fluid from the upper motor chambers 23a and 24a passing through the exhaust passageway 54a, will be forced outwardly through the apertures 35 and upwardly through the casing annulus around the insert tubing string 2l. Also during the upstroke of the pump pistons, a suction is created in the chambers 55]? and Sub. Well fluids will then enter through the standing valve assembly 74 and directly fill the lower chamber 56h. The well liuids will also pass'upwardly through the interior of the pump connecting rod 59, and the bores Still and fill the chamber 55h. Also, any uids which may have accumulated in the chamber 56a, by seepage past the piston rings lll-4l or by any other access route, will force the spring biased check valve 292 open and pass into the passageway 288.

Upon approaching the upper limit of the upstroke, the annular washer 269 will contact the shoulder 264. The washer 260 will be moved relatively downwardly to compress the spring 262 and move the striker pin member 224 downwardly to unseat the ball valve 222. When the ball valve 222 is unseated, high pressure fluid will be applied to the upper end of the pilot valve member 23d) through the passageway means comprised of the passageway 2.118, the passageway y216, and the passageway 214 to the upper end of the pilot valve cavity. A portion of the high pressure power fluid will pass through the orifice sleeve 338 through the passageway 23d, and through the bore 254 to the low pressure port 250. However, the orifice sleeve 338 causes a sufcient pressure drop that the high power huid pressure applied to the upper end of the upper -pilot valve member 230 is not appreciably reduced. lt will be recalled that the interior of the central portion of the pilot valve cavity is at low or exhaust pressure, because the exhaust port 256 is open, while the lower end of the lower pilot valve member 226 is subjected to high power fluid pressure within the chamber 24h. However, the cross sectional area of the upper pilot valve member 230 is greater than the cross sectional area of the lower pilot valve member 226, and the fluid pressure maintained above the upper pilot valve member 23@ by the restrictive orifice is sullcient that both the upper and lower pilot valve members 230 and 226 will be shifted downwardly by the net hydraulic force on the pilot valve assembly. After a short distance of travel of the upper pilot valve member 230, the port 254 is closed so that the pressure above the upper pilot valve member 23@ is increased to power uid pressure. Also, the lower end of the upper pilot valve member 230 closes the bore 256 after a short distance of travel so that the fluid in the pilot valve cavity around the portion 228 of the lower pilot valve member 226 and in the main valve control cavity 204 will be trapped. The pressure of the trapped fluid will quickly be increased substantially to that of the high pressure power uid above the upper pilot valve member 230, and the main valve it) will be moved upwardly by the force of the hydraulic fluid in the main valve control cavity 2M, as the upper pilot valve member 230 moves downwardly. When the pilot valve assembly has reached its lower limit of travel, the high pressure port 24S will be opened and high pressure power uid will be passed from the -port 240 through the port 2453, around the portion 228 of the lower pilot valve member 226, and through the passageway 205 to the main valve control cavity 204 to completely shift the main valve 13@ to the upper position and hold it in this position.

When the main valve i3d has reached the upper position, the high pressure power fluid in the high pressure annular passageway 250 is directed to the upper motor chambers 24a and 23a by the fluid passageway means comprised of the annular groove 17S, the radial bores 165 and 164, to the chamber 2da, and the apertures 116, the annular passageway 113, and the bores 126 and 124 to the chamber 23a. At the same time, the lluid within the chamber 2419 is vented to the exhaust liuid passageway .54a through the fluid passageway means comprising the bore 160, the radial bores 180, and the interior passageway 17? of the main valve 130. The net hydraulic force of the upper motor piston 25 is downwardly due to the greater area of the upper working surface of the piston 25, as previously described. The net hydraulic force acting on the lower motor piston 26 is also directed downwardly since high pressure power fluid is acting on the upper working surface thereof and low pressure exhaust fluid is acting on the lower working surface. Therefore, the motor pistons 25 and 26, and of course the pump pistons 57 and 58, will move downwardly through a downstroke.

During the downstroke, the main valve 13@ is assured of being maintained in its up position and the pilot valve assembly is assured of being maintained in its down position because of the following conditions. As soon as the main valve 13@ reached its uppermost position, the pressure of the fluid in the chamber 24b acting on the lower end of the lower pilot valve member 226 was reduced to exhaust pressure. When the pilot valve assembly is shifted downwardly, the two low pressure ports 254 and 256 are closed by the upper pilot valve member 230. Also, the upper high pressure port 246 is opened and continually assures that high pressure fluid is maintained in the pilot valve cavity above the upper pilot valve member 230. Similarly, the lower pilot valve member 226 is moved downwardly sufficiently to uncover the lower high pressure port 2&8, and high pressure fluid passes around the portion 228 of reduced diameter and through the port 265 into the main valve shifting cavity 204, which insures that the main valve is maintained in the up position. The

pilot valve assembly 225 is maintained in the down position with the lower end thereof abutting the shoulder 268 by the high pressure fluid at the upper end of the lower pilot valve member 226 which acts against low pressure exhaust fluid in the chamber 24h. High pressure power fluid will act against both ends of the upper pilot valve member 230, but once the member 239 is shifted, it will be retained in the lower position by friction. The high pressure port 246 is open during the downstroke to insure that the pressure remains equalized at each end of the upper pilot valve member ,230.

During the downstroke of the pump pistons 57 and 53, the standing valve 32, which is a downwardly closing check valve, will be closed to prevent the lluid already within the pump unit from being forced out. As the lower pump piston 558 moves downwardly, the check valve 292 will be closed to prevent lluid from passing upwardly through the passageway 290 into the chamber 56a above the lower pump piston 58. Therefore, all fluid in the lower pump cylinder sleeve 7? below the lower pump cylinder 96 will be displaced and forced upwardly through the passageway 2.88, through the interior passageway 59a of ,the .connecting `rod 59, and through the traveling valve 28-0 into the chamber 55a above the upper pump piston 57. Similarly, all fluid within the chamber 55h below the upper pump piston 57 will be displaced and forced through the radial bores 30u into the interior passageway 280a and upwardly by the open traveling valve 280. The displaced well fluids from the chambers 56h and 55b which pass through the traveling valve assembly 274 will commingle with the exhaust iluid passing from the chamber 24b downwardly through the passageway 54a and the total fluid will exit through the apertures 35 and be pumped upwardly through the casing annulus.

As the lower motor piston 26 approaches the bottom of the downstroke, the lower end of the lower pilot valve striker member 226 will contact the upper end 2li (see FIG. 2) of the packing housing 46 and mechanically shift the pilot valve assembly upwardly until the exhaust port 256 is opened and the high pressure ports 246 and 24S are closed. rlChe fluid Vin the main valve control cavity 204 will be reduced to .exhaust iiuid pressure through the passageway 205, the pilot valve cavity, the port 256, the exhaust fluid port 250 and the passageway 258. The pressure differential acting on the main valve 130 will then shift the main valve downwardly to the lower position as previously described to cause an upstroke of the pistons. As the pressure of the fluid in the chamber 24h below the lower motor piston 26 builds, the high pressure power fluid will act on the lower end of the lower pilot valve member 226. The low pressure port 254 will register with' the passageway 234 so that the pressure above the upper pilot valve member 230 will be exhaust pressure which will cause the ball valve 222 to close. 'Ihe high pressure power fluid acting on the bottom of the lower pilot valve member 226 will overcome the low pressure now acting on the upper end of the upper pilot valve member 230, and the pilot valve assembly 225 will be shifted to the upper position. This also insures that throughout the upstroke any high pressure which may leak by the ball valve 222, or pass from the high pressure port 246 to the pilot valve cavity above the upper pilot valve member 230, will be vented to exhaust pressure so that the high pressure acting on the lower end of the lower pilot valve member 226 will maintain the pilot valve assembly in the up position during the upstroke of the piston members. This cycle of events will repeat indefinitely so long as the power fluid is supplied through the insert tubing string 21.

From the above detailed description of a preferred embodiment of the present invention, it will be evident that a pumping unit having great efficiency and therefore economy of operation has been described. The upper motor piston 25 is a differential type piston and produces approximately equal thrust on both the upstroke and the downstroke. The lower motor piston 26 is, by reason of the four-way valve 130, a double acting piston and produces equal thrust on the upstroke and downstroke, provided the connecting rods at either end thereof are of equal diameter. The total working area of the complex fluid motor is approximately double that available in a single piston fluid motor having the same available outside diameter. Further, the use of the tubular main valve 130 provides greater fluid passageway areas to reduce pressure losses as the power fluid and exhaust fluid pass through the various passageway means. Since the fluid motor delivers approximately equal thrust during the up and down strokes, the complex pump may be designed for maximum efficiency. Although three separate valve members are utilized in the lower motor piston 26, each of the valve members is of the simplest possible construction, and can be economically manufactured. The main valve is a single piece valve and is disposed within a valve cavity formed in the body of the lower motor piston 26. The pilot valve assembly is formed in two parts, and therefore can be easily manufactured. Since the pilot valve assembly is in two parts, the pilot valve cavity formed by the bore 206 and the counterbore 212 do not need to be precisely aligned, which reduces cost of manufacture. All of the various ports associated with the pilot valve assembly are merely bores drilled in the body 133 of the motor piston 26. The ball valve 222 and striker pin 224 are of simple and economical construction. The mechanisms for bumping and mechanically shifting the lower pilot valve member 226 upwardly is very simple, as is the mechanism for unseating the ball valve 222.

Having thus described a preferred embodiment of the invention, it will be evident to those skilled in the art that various changes and substitutions can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

What is claimed is:

1. In a fluid motor having a cylinder member and a piston member disposed therein and reciprocated by alternately applied high and low fluid pressure, 'the application of which is controlled by a main valve means operatively disposed therein for causing reciprocation of the piston member when shifted between first and second positions, the main valve means having a control working area such that when low pressure fluid is applied to the control working area the main valve means will be shifted to the first position, and when high pressure fluid is applied to the control Working area the main valve means will be shifted to the second position, an improved pilot valve assembly for controlling the shifting of the main valve comprising:

a control fluid passageway means in the piston member for providing fluid communication between the pilot valve cavity and the control working area,

high pressure fluid passageway means for providing fluid communication between a source of high pressure fluid and the pilot valve cavity;

low pressure fluid passageway means for providing fluid communication between a source of low pressure fluid and the pilot valve cavity,

a pilot valve means operatively positioned in the pilot valve cavity for, when in a second position, placing the high pressure fluid passageway means in fluid communication with the control fluid passageway means and alternatively, when in a first position, for placing the low pressure fluid passageway means in fluid communication with the control fluid passageway means,

said pilot valve means also having a restricted passageway extending therethrough providing communication between the pilot valve cavity connected with said source of high pressure fluid and the low pressure fluid passageway means to prevent inadvertent shifting of said pilot valve means from the first to the second position;

and means for shifting the pilot valve means from one position to the other as the pistom member approaches the ends of the cylinder member.

2. A fluid motor for a subsurface pump unit comprisfirst and second interconnected cylinder members aligned in tandem relationship;

first -and second piston members reciprocall',r disposed in the first and second cylinder members, respectively, and having first working areas facing in one direction and second working areas facing in the opposite direction;

a first piston rod means interconnecting the first and second working areas of the first and second piston members, respectively;

a second piston rod means connected to the second working area of the first piston member and extending through the end of the second cylinder member for connection to a pump piston;

fluid passageway means for continuously applying high pressure fluid to the second working area of the second piston means; and,

Valving means disposed in the piston members and connecting rod means for, alternately, applying power fluid to the second working area of the first piston member while exhausting fluid from the first working areas of the first and second piston members, and then applying power fluid to the first working areas of the first and second piston members while exhausting fluid from the second working area of the first piston member.

3. A fluid motor for a subsurface pump unit comprising:

a cylinder member;

a piston member reciprocally disposed in the cylinder member;

said piston member having a first working area facing one end of the cylinder member and a second working area facing the opposite end of the cylinder member;

a first piston rod means connected to the piston member and extending through one end of the cylinder member;

a second piston rod means connected to the piston member and extending through the other end of the cylinder member;

a valve cavity in the piston member;

power fluid passageway means through the first piston rod means for providing fluid communication between a source of power fluid and the valve cavity;

exhaust fluid passageway means through the second piston rod means for providing fluid communication between the valve cavity and an exhaust fluid outlet;

first fluid passageway means in the piston member for providing fluid communication between the valve cavity and the first working area;

second fluid passageway means in the piston member for providing fluid communication between the valve cavity and lthe second working area;

valve means positioned in the valve cavity and operatively connected to the piston member for placing the power fluid passageway means in fluid communication with the first fluid passageway means and placing the exhaust fluid passageway means in fluid communication with the second fluid passageway means and, alternately, upon shifting of the valve means, for placing the power fluid passageway means in fluid communication with the second fluid passageway means and for placing the exhaust fluid passageway means in fluid communication with the first fluid passageway means to cause reciprocation of the piston member upon shifting of the valve means;

said valve means comprising a differential area piston valve having a control working area thereon, said piston valve comprising a sleeve having a longitudinally extending fluid passageway therethrough in communication at all times with the exhaust fluid passageway and having a second area thereon constantly in communication with said power fluid passageway, said second area being of less area than the area of said control working area, the piston valve being shifted to one position when the control working area is in communication with said exhaust fluid passageway and to the other position when the control working area is in communication with said fluid power passageway; and

pilot valve means operably disposed in said piston member to provide communication through said power fluid passageway to said valve cavity adjacent to said control working area and to provide communication through said exhaust fluid passageway to said valve cavity adjacent to said control working area.

4f. A fluid motor for a subsurface pump as dened in claim 3 further characterized by:

a pilot valve cavity in the piston member;

a control fluid passageway means in the piston member f for providing fluid communication between the pilot valve cavity and the control working area on the piston valve;

a rst pilot fluid passageway means in the piston member for providing fluid communication between the power fluid passageway means and the pilot valve cavity;

a second pilot fluid passageway means in the piston member for providing fluid communication between the exhaust fluid passageway means and the pilot valve cavity;

and a pilot valve member operatively positioned in the` pilot valve cavity for placing, when in one position, the control fluid passageway in fluid communication with the first pilot fluid passageway and, alternatively, when in another position, for placing the control fluid passageway means in fluid communication with the second pilot fluid passageway.

5. A fluid motor for a subsurface pump unit comprising:

1 a cylinder member;

a piston member reciprocally disposed in the cylinder member;

said piston member having a first working area facing one end of the cylinder member and a second working area facing the opposite end of the cylinder member;

a first piston rod means connected to the piston member and extending through one end of the cylinder member;

a second piston rod means connected to the piston member and extending through the other end of the cylinder member;

a valve cavity in the piston member;

power fluid passageway means through the first piston rod means for providing fluid communication between a source of power fluid and the valve cavity;

exhaust fluid passageway means through the second piston rod means for providing fluid communication between the valve cavity and an exhaust fluid outlet;

first fluid passageway means in the piston member for providing fluid communication between the valve cavity and the first working area;

second fluid passageway means in the piston member for providing fluid communication between the valve cavity and the second working area;

valve means positioned in the valve cavity and operatively connected to the piston member for placing the power fluid passageway means in fluid communication with the first fluid passageway means and placing the exhaust fluid passageway means in fluid communication with the second fluid passageway means and, alternately, upon shifting of the valve means, for placing the power fluid passageway means in fluid communication with the second fluid passageway means and for placing the exhaust fluid passageway means in fluid communication with the first fluid passageway means to cause reciprocation of the piston member upon shifting of the valve means;

said valve means comprising a sleeve having a longitudinally extending fluid passageway therethrough; and

the longitudinally extending fluid passageway therethrough is in fluid communication at all times with the exhaust fluid passageway means.

6. A fluid motor for a subsurface pump unit comprising:

a cylinder member;

a piston member reciprocally disposed in the cylinder member;

said piston member having a first working area facing one end of the cylinder member and a second working area facing the opposite end of the cylinder member;

a first piston rod means connected to the piston member and extending through on@ end of the cylinder member;

a second piston rod means connected to the piston member and extending through the other end of the cylinder member;

a valve cavity in the piston member;

power fluid passageway means through the first piston rod means for providing fluid communication between a source of power fluid and the valve cavity;

exhaust fluid passageway means through the second piston rod means for providing fluid communication between the valve cavity and an exhaust fluid outlet;

first fluid pasasgeway means in the piston member for providing fluid communication between the valve cavity and the first working area;

second fluid passageway means in the piston member for providing fluid communication between the valve cavity and the second working area;

valve means positioned in the Valve cavity and operatively connectedto the piston member for placing the power fluid passageway means in fluid communication with the first fluid pasasgeway means and 17 placing the exhaust lluid passageway means in fluid communication with the second fluid passageway means and, alternately, upon shifting of the valve means, for placing the power uid passageway means in liuid communication with the second fluid passageway means and for placing the exhaust fluid passageway means in fluid communication with the first iiuid passageway means to cause reciprocation of the piston member upon shifting of the valve means;

a second cylinder member aligned in tandem relation with the cylinder member;

a second piston member reciprocally disposed in the second cylinder member and having a first working area facing in the same direction as the iirst working area of the piston member and a second working area facing in the opposite direction;

the rst piston rod member passing into the second cylinder member and being connected to the second piston member at the second working area thereof;

third fluid passageway means in the first piston rod member and second piston member for providing uid communication between the rst working areas of the two piston members; and

wherein the power iiuid passageway means includes uid passageway means in the second cylinder member providing fluid communication between a source of power fluid and the second working area of the second piston member, and lluid passageway means in the second piston member for providing fluid communication between the second working area of the second piston member and the power fluid passagway means through the irst piston rod means.

7. A iiuid motor for a subsurface pump unit comprising:

a cylinder member;

a piston member reciprocally disposed in the cylinder member;

said piston member having a first working area facing one end of the cylinder member and a second working area facing the opposite end of the cylinder member;

a first piston rod means connected to the piston member and extending through one end of the cylinder member;

a second piston rod means connected to the piston member and extending through the other end of the cylinder member;

a valve cavity in the piston member;

power fluid passageway means through the rst piston rod means for providing fluid communication between a source of power fluid and the valve cavity;

exhaust fluid passageway means through the second piston rod means for providing fluid communication between the valve cavity and an exhaust fluid outlet;

first fluid passageway means in the piston member for providing uid communication between ther valve cavity and the rst working area;

second fluid passageway means in the piston member for providing fluid communication between the valve cavity and the second working area;

valve means positioned in the valve cavity and operatively connected to the piston member for placing the power fluid passageway means in fluid communication with the first fluid passageway means and placing the exhaust fluid passageway means in fluid communication with the second fluid passageway means, and, alternately, upon shifting of the valve means, for placing the power uid passageway means in uid communication with the second fluid passageway means and for placing the exhaust uid passageway means in fluid communication with the first iluid passageway means to cause reciprocation of the piston member upon shifting of the valve means;

said valve means comprising a differential area piston valve having a control working area thereon, the piston valve being shifted to one position when a low pressure is applied against the control working area and to the other position when a high pressure is applied against the control working area;

a pilot valve cavity in the piston member;

a control fluid passageway means in the piston member for providing fluid communication between the pilot valve cavity and the control working area on the piston valve;

a irst pilot fluid passageway means in the piston member for providing fluid communication between the power uid passageway means and the pilot valve cavity;

a second pilot fluid passageway means in the piston member for providing fluid communication between the exhaust fluid passageway means and the pilot valve cavity;

a pilot valve means operatively positioned in the pilot valve cavity for placing, when in one position, the control fluid passageway in fluid communication with the first pilot iiuid passageway and, alternatively, when in another position, for placing the control uid passageway means in fluid communication with the second pilot iluid passageway; and,

means for shifting said pilot valve means comprising:

first means for mechanically moving the pilot valve means as the piston approaches one end of the cylinder to cause a shift thereof from one position to the other, and

second means including pilot actuating valve means operably disposed in the first pilot fluid passageway for controlling uid passage therethrough to the pilot valve cavity and second mechanical means for opening the pilot actuating valve means as the piston approaches the other end of the cylinder for applying power fluid to the pilot valve means to shift the pilot valve means to the first position.

8. In a uid motor having a cylinder member and a piston member disposed therein and reciprocated by alternately applied high and low fluid pressure, the application of which is controlled by a main valve means operatively disposed therein for causing reciprocation of the piston member when shifted between first and second positions, the main valve means having a control working area such that when low pressure fluid is applied to the control working area the main valve means will be shifted to the rst position, and when high pressure fluid is applied to the control working area the main valve means will be shifted to the second position, an improved pilot valve assembly for controlling the shifting of the main valve comprising:

a control uid passageway means in the piston member for providing uid communication between the pilot valve cavity and the control working area,

high pressure fluid passageway means for providing fluid communication between a source of high pressure fluid and the pilot valve cavity;

low pressure fluid passageway means for providing uid communication between a source of low pressure fluid and the pilot valve cavity;

a pilot valve means operatively positioned in the pilot valve cavity for, when in a second position, placing the high pressure fluid passageway means in iiuid communication with the control uid passageway means, and, alternatively, when in a rst position, for placing the low pressure iiuid passageway means in iluid communication with the control tiuid passageway means; and,

means for shifting the pilot valve means from one position to the other as the piston member approaches 19 the ends of the cylindrical member; said means including:

rst bumper means for mechanically moving the pilot valve means from one position as the piston member approaches one end of the cylindrical member, said high pressure fluid passageway means providing uid communication between said source of high pressure and the pilot valve cavity for shifting the pilot valve means from the other position when high pressure fluid is applied thereto, pilot actuating valve means for controlling passage of high pressure lluid through said high pressure iluid passageway means, and second bumper means for mechanically opening the pilot actuating valve means as the piston member approaches the other end of the cylinder member,

whereby as the bumper means strike opposite ends of the cylinder member, the pilot valve assembly will be shifted to cause a shifting of the main valve and a reciprocation of the piston member.

References Cited by the Examiner UNITED STATES PATENTS 15 FRED E. ENGELTHALER, Primary Examiner.

KARL J. ALBRECHT, SAMUEL LEVINE, Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,204,535 Septembery 7, 1965 Charles L. English It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 7, line 2l, before "portion", first occurrence, insert Case 1n practice, that cross sectional area of the upper Signed and sealed this 15th day of March 1966.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD I. BRENNER Attesting Officer Commissioner of Patents 

1. IN A FLUID MOTOR HAVING A CYLINDER MEMBER AND A PISTON MEMBER DISPOSED THEREIN AND RECIPROCATED BY ALTERNATELY APPLIED HIGH AND LOW FLUID PRESSURE, THE APPLICATION OF WHICH IS CONTROLLED BY A MAIN VALVE MEANS OPERATIVELY DISPOSED THEREIN FOR CAUSING RECIPROCATION OF THE PISTON MEMBER WHEN SHIFTED BETWEEN FIRST AND SECOND POSITIONS, THE MAIN VALVE MEANS HAVING A CONTROL WORKING AREA SUCH THAT WHEN LOW PRESURE FLUID IS APPLIED TO THE CONTROL WORKING AREA THE MAIN VALVE MEANS WILL BE SHIFTED TO THE FIRST POSITION, AND WHEN HIGH PRESSURE FLUID IS APPLIED TO THE CONTROL WORKING AREA THE MAIN VALVE MEANS WILL BE SHIFTED TO THE SECOND POSITION, AN IMPROVED PILOT VALVE ASSEMBLY FOR CONTROLLING THE SHIFTING OF THE MAIN VALVE COMPRISING: A CONTROL FLUID PASSAGEWEAY MEANS IN THE PISTON MEMBER FOR PROVIDING FLUID COMMUNICATION BETWEEN THE PILOT VALVE CAVITY AND THE CONTROL WORKING AREA, HIGH PRESSURE FLUID PASSAGEWAY MEANS FOR PROVIDING FLUID COMMUNICATION BETWEEN A SOURCE OIF HIGH PRESSURE FLUID AND THE PILOT VALVE CAVITY; LOW PRESSURE FLUID PASSAGEWAY MEANS FOR PROVIDING FLUID COMMUNICATION BETWEEN A SOURCE OF LOW PRESSURE FLUID AND THE PILOT VALVE CAVITY, A PILOT VALVE MEANS OPERATIVELY POSITIONED IN THE PILOT VALVE CAVITY FOR, WHEN IN A SECOND POSITION, PLACING THE HIGH PRESSURE FLUID PASSAGEWAY MEANS IN FLUID COMMUNICATION WITH THE CONTROL FLUID PASSAGEWAY MEANS AND ALTERNATIVELY, WHEN IN A FIRST POSITION, FOR PLACING THE LOW PRESSURE FLUID PASSAGEWAY MEANS IN FLUID COMMUNICATION WITH THE CONTROL FLUID PASSAGEWAY MEANS, SAID PILOT VALVE MEANS ALSO HAVING A RESTRICTED PASSAGEWAY EXTENDING THRETHROUGH PROVIDING COMMUNICATION BETWEEN THE PILOT VALVE CAVITY CONNECTED WITH SAID SOURCE OF HIGH PRESSURE FLUID AND THE LOW PRESSURE FLUID PASSAGEWAY MEANS TO PREVENT INADVERTENT SHIFTING OF SAID PILOT VALVE MEANS FROM THE FIRST TO THE SECOND POSITION; AND MEANS FOR SHIFTING THE PILOT VALVE MEANS FROM ONE POSITION TO THE OTHER AS THE PISTOM MEMBER APPROACHES THE ENDS OF THE CYLINDER MEMBER. 